docs: def _build(self, parent_cache):
          """Build the initial cache from the parent.
  
          Only include the |MICE| which are unaffected by the subsystem cut.
          A |MICE| is affected if either the cut splits the mechanism
          or splits the connections between the purview and mechanism
          """
          for key, mice in parent_cache.cache.items():
              if not mice.damaged_by_cut(self.subsystem):
                  self.cache[key] = mice